Thanks, Lance, I'll investigate ebay.
At close of play today I have an engine and a cockpit interior.

I haven't and aren't going to fit spark plug leads. It seems like a right faff for something that won't be seen when the engine's under the cowling and I'd rather quit whilst I'm ahead and not risk messing it up.

I trial-fitted it in the fuselage halves, with the engine mounting plate and the cockpit top held in place with masking tape. It all seemed to line up properly so I'm happy with that.
I'm going to put it aside and do something else until I have the tools to continue and try and do a proper job of it.
I didn't mention which version I'm doing. It's going to be N6171 'Black Arrow' of Naval 3.